The present invention relates to a circuitry which is used for detecting a fault current on the supply line of an electronic circuit and which is equipped with an auxiliary voltage source and a potential monitor for determining and analyzing the potential prevailing on the supply line during a testing period.
German patent application No. 42 42 177 discloses a circuitry of this type which is used to monitor a large number of valve coils and their associated final stages. For fault current detection, an auxiliary voltage source is connected to the common supply line for the valve coils by way of a high-ohmic resistor, and the potential on the supply line is measured and analyzed. Before this action, the connection of the supply line to the supply source, i.e., the vehicle battery, was interrupted by way of a semiconductor relay. The associated potential monitor is connected by way of a high-ohmic voltage divider. When a shunt circuit or a leakage current from the supply line to the supply source or to ground occurs, the potential on the supply line will vary.
An object of the present invention is to provide a circuitry of this type which has a high degree of accuracy, sensitiveness and reliability in the detection of fault currents, which also includes leakage currents, and, in addition, can be realized with comparatively little effort. A simple and, hence, low-cost measuring apparatus for monitoring the potential on the supply line is deemed sufficient.